1. The Field of the Invention
The present invention is related to the degradation of environmentally persistent organic compounds. More particularly, the present invention employs a lignin-degrading fungus (a white rot fungi), or the biodegrading enzyme system produced by a fungi, in order to degrade the environmentally persistent organic compounds.
2. The Prior Art Background
Large quantities of environmentally persistent organic compounds have been disposed of in the biosphere. The term "environmentally persistent" or "persistent" organic compounds is used herein to include those organic compounds which are only slowly degraded, if they are degraded at all, in the natural environment. Unfortunately, the effects of the environment, including the action of microorganisms, are not sufficient to degrade and dispose of these organic compounds.
Because of the slow degradation of such organic compounds, they present extreme problems in disposal. One such category of environmentally persistent organic compounds comprises organohalides. Other categories of such persistent organic compounds include aromatic organic compounds, particularly cyclic and polycyclic aromatic organics.
Persistent organic compounds, such as organohalides, are a serious threat to the environment because they are often toxic and carcinogenic. Moreover, since they are difficult to degrade and are not easily metabolized, these compounds tend to "bioaccumulate" in the body fat of animals occupying higher trophic levels.
Some of the organohalide compounds which have been found to pose particular problems include polychlorinated biphenyls (PCB) and polybrominated biphenyls ("PBB"). Since these compounds have been important to twentieth century manufacturing, they are today found to be present in river beds, landfills, and other disposal sites near industrial centers.
In addition, PCB's have been used extensively in electrical transformers and in various lubricants and oils Thus, disposal sites for these materials and equipment often contain large concentrations of PCB's and other organohalides. Other types of environmentally persistent molecules include DDT, dioxin, and many pesticides.
Attempts have been made to remove and degrade environmentally persistent compounds such as the organohalides of the type mentioned above. For example, it has been suggested that materials of this type be incinerated.
Indeed, attempts have been made to burn PCB's and other related compounds. It has, been found, however, that incineration is usually impractical where there are large volumes of waste to be processed or where the matrix of material contained in the compound is difficult to process. For example, PCB-contaminated soil would be difficult to process using an incineration procedure. In addition, incineration must take place far from population centers. Accordingly, transportation and processing costs become very high.
Other attempts to clean up disposal sites containing organohalides and other complex organics have focused on simple removal and/or isolation of the material. For example, soil containing contamination is excavated and moved to an approved hazardous waste disposal site.
Problems with this method are clear. Removal does nothing to degrade or remove the pollutant. Removal simply changes the location of the pollutant. An additional problem with removal procedures is the expense. Excavation of large quantities of soil contaminated by DDT, dioxin, PCB, or the like, is extremely difficult, time-consuming and expensive. The material once excavated must then be transported to a certified hazardous waste disposal site. All of this makes removal a technically difficult, expensive, and often impractical process.
One additional alternative is degradation of these pollutants through the use of microorganisms. Unfortunately, few microorganisms have any significant effect on halogenated organic compounds. Those microorganisms which do, however, are only able to metabolize halogenated organic compounds partially and selectively, and are frequently affected by the intermediate compounds encountered in the biodegradation process. The intermediates produced through biodegradation may themselves be extremely toxic to both the microorganism and other organisms in the environment.
Some efforts to use microorganisms have focused on strategies to enhance the relative abilities of these organisms to degrade various persistent xenobiotics. For example, there have been a number of studies in which microorganisms have been adapted to grow on carbon sources whose structure resembles the organic pollutant under study. When the microorganism is presented with a structurally similar organic pollutant, it theoretically is often also metabolized. This is known as "analog induced" metabolism.
Others have attempted to culture microorganisms using the organic pollutant itself as the source of carbon. It is intended that isolated strains could be used to inoculate areas in the environment that have been contaminated with the pollutant in question.
Still other studies have focused on the use of anaerobic organisms. This strategy has been adopted because many organic pollutants are found in lake and river sediments and landfills, sites where oxygen availability is limiting.
Problems have been encountered in each of these approaches. Most of these prior art microorganisms have been unable to degrade all pollutants which they encounter. Most microorganisms are selective, rather than nonselective, in their action. Thus, mixtures of pollutants are not effectively treated using these microorganisms.
Accordingly, it would be a significant advancement in the art if a system could be provided for employing a nonspecific microorganism system to degrade other organic compounds, such as organic pollutants. It would be a major advancement in the art to provide an enzyme system to degrade PCB's, PBB's, dioxin, DDT, and the like. It would be another advancement in the art to provide a system whereby the fungus itself could be used in environmental control. It would be a related advancement if, in such a system, the fungus itself could be introduced to the polluted soil or other polluted site to degrade the subject pollutants.
Such methods are disclosed and claimed herein.